The present invention relates to a frequency-changeable microwave signal generator.
Conventional microwave signal communication units and radar units often employ a single designated transmitting or receiving frequency. However, demand has recently arisen to change the transmitting or receiving frequency at predetermined intervals within a predetermined frequency band. To satisfy such demand for a microwave signal generator having a high frequency stability, a synthesizer-type microwave signal generator having a quartz oscillator as a reference is conventionally available. With this generator, however, the number of components is large and hence the circuit configuration is complex, resulting in a considerably large generator. Therefore, this conventional generator is not suited for incorporation in an actual system.
In order to solve these problems, generally, a required number of small, high frequency-stabilized microwave signal generators are provided, and are switched as needed. FIG. 1 shows a circuit diagram of a microwave signal generator according to this method.
Referring to FIG. 1, microwave signal oscillators 1-1 to 1-n having oscillating frequencies fl to fn, respectively, are connected to band-pass filters 2-1 to 2-n via transmission lines 3. The center frequencies of the passbands of these band-pass filters are set to fl to fn, respectively. Transmission lines 3 can be comprised of micro strip lines or the like. Filters 2-1 to 2-n are connected through further transmission lines 3 to circulators 4-1 to 4-n, respectively. Circulators 4-1 to 4-n are series-connected via transmission lines, and output port 5 connected to circulator 4-1 generates microwave power. Power supply V.sub.B is supplied to oscillators 1-1 to 1-n via switches 6-1 to 6-n, to operate them.
In the microwave signal generator having the above arrangement, when a microwave signal output of frequency fn is to be obtained, only switch 6-n is turned on, and all remaining switches 6-1 to 6-(n-1) are turned off. Then, a microwave signal of frequency fn is generated from oscillator 1-n, and is supplied to circulator 4-(n-1) through filter 2-n and circulator 4-n. Subsequently, the microwave signal of frequency fn is supplied to filter 2-(n-1) from circulator 4-(n-1) through transmission line 3, is reflected by filter 2-(n-1), and is returned to circulator 4-(n-1). This operation is repeated to generate a microwave signal of frequency fn from output port 5. When the microwave signal generator generates a microwave signal of another frequency, ON/OFF operation of switches 6-1 to 6-n is performed in the same manner, to enable a corresponding one of oscillators 1-1 to 1-n, thereby generating a microwave signal at a predetermined frequency.
However, the microwave signal generator of the above arrangement requires n filters and n circulators, resulting in a considerably large outer size. Furthermore, since the number of components is large, the reliability of the generator is degraded.
According to another conventional system, PIN diode switches are used in place of the circulators in the above microwave signal generator, and are interlinked with a power supply circuit switch (Japanese Patent Publication No. 60-11843). With this system, again, the circuit configuration is complex, and the number of components is large, resulting in a degraded reliability.